Field of the Invention
The present invention relates to a liquid crystal display, and more particularly, to a liquid crystal display having a low speed driving mode.
Discussion of the Related Art
Various flat panel displays, such as a liquid crystal display (LCD), a plasma display panel (PDP), an organic light emitting diode (OLED) display, and an electrophoresis display (EPD), have been developed. A liquid crystal display displays an image by controlling an electric field applied to liquid crystal molecules based on a data voltage. An active matrix liquid crystal display includes a thin film transistor (TFT) in each pixel.
A liquid crystal display may include a liquid crystal display panel, a backlight unit irradiating light onto the liquid crystal display panel, source driver integrated circuits (ICs) for supplying a data voltage to data lines of the liquid crystal display panel, gate driver ICs for supplying gate pulses (or scan pulses) to gate lines (or scan lines) of the liquid crystal display panel, a control circuit for controlling the source driver ICs and the gate driver ICs, a light source driving circuit for driving light sources of the backlight unit, and the like.
When a DC voltage is applied to the liquid crystal in a liquid crystal display, image persistence may be generated. The image persistence is a phenomenon in which a previous image is seen although a screen image has been updated. The image persistence appears more prominently when a static image is displayed on the liquid crystal display for a long period of time or an application time of the DC voltage applied to the liquid crystals increases. An example of a mechanism generating the image persistence is a phenomenon in which impurity ions in a liquid crystal layer are accumulated on an alignment layer for setting a pretilt angle of liquid crystal molecules. Negatively charged ions and positively charged ions based on a polarity of an electric field applied to the liquid crystal molecules move along a motion vector and are polarized in opposite directions. Because the motion vector is not changed, an amount of impurity ions accumulated on the alignment layer increases as time passes. An increase in the amount of impurity ions affects a movement characteristic tending to return to an initial alignment state of the liquid crystal molecules, thereby generating the image persistence.
A liquid crystal display may operate in a low speed driving mode so as to reduce power consumption and may reduce a frame rate or a frame frequency when an input image is a static image. However, when the frame frequency is reduced, a luminance may be suddenly changed each time the data voltage is changed. Further, because a voltage discharge time of the pixel increases, a flicker phenomenon, in which the image flickers, may be generated.
Moreover, the low speed driving mode is susceptible to the image persistence problem because the application time of the DC voltage applied to the liquid crystal increases. Thus, there is a need for a method capable of preventing or lessening a reduction in image quality of the liquid crystal display in the low speed driving mode.